perf(android): low-latency decode overhaul — vendor keys, async loop, system tuning

Close the latency gap on the Android client with per-SoC decoder tuning, an
event-driven decode loop, and full system integration.

- Decoder selection: rank MediaCodecList decoders in Kotlin (hardware/vendor
  preferred, software avoided, FEATURE_LowLatency probed) and create the chosen
  one by name. Per-SoC low-latency keys gated on the codec-name prefix: Qualcomm
  picture-order + low-latency, Exynos (also Google Tensor), Amlogic, HiSilicon;
  MediaTek vdec-lowlatency set unconditionally. operating-rate = MAX (Qualcomm)
  vs priority = 0 (else) are mutually exclusive. NVIDIA/Rockchip/Realtek have no
  vendor key — covered by ranking + the standard low-latency key.

- Async decode loop: AMediaCodec async-notify replaces the poll loop, presenting a
  decoded frame the instant it is ready instead of waiting out a poll interval.
  Behind USE_ASYNC_DECODE with the synchronous loop kept for A/B during bring-up.

- System integration: Wi-Fi FULL_LOW_LATENCY lock and HDMI ALLM
  (setPreferMinimalPostProcessing) for the stream's lifetime; game_mode_config.xml
  opting out of OEM downscaling / FPS overrides.

- Pipeline: boost the data-plane pump + audio thread priorities, AAudio usage=Game,
  DSCP marking on by default on Android, ADPF setPreferPowerEfficiency(false),
  and setFrameRateWithChangeStrategy(ALWAYS) to force the HDMI mode switch on TV.

- lowLatencyMode master toggle (default on) as the escape hatch; the stats HUD now
  shows the resolved decoder name.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/android/native/src/audio.rs

@@ -18,8 +18,8 @@
 //! grown on XRuns (Google's anti-glitch technique).
 
 use ndk::audio::{
-    AudioCallbackResult, AudioDirection, AudioFormat, AudioPerformanceMode, AudioSharingMode,
-    AudioStream, AudioStreamBuilder,
+    AudioCallbackResult, AudioContentType, AudioDirection, AudioFormat, AudioPerformanceMode,
+    AudioSharingMode, AudioStream, AudioStreamBuilder, AudioUsage,
 };
 use punktfunk_core::client::NativeClient;
 use punktfunk_core::error::PunktfunkError;
@@ -235,6 +235,11 @@ impl AudioPlayback {
                 // captures + Opus-encodes in exactly this order.
                 .channel_count(channels as i32)
                 .format(AudioFormat::PCM_Float)
+                // Tag the stream as game audio (usage=Game / content=Movie): the audio HAL applies
+                // its low-latency game-audio routing/policy and it's grouped correctly with the
+                // game-mode profile. Advisory — ignored where the device has no such policy.
+                .usage(AudioUsage::Game)
+                .content_type(AudioContentType::Movie)
                 .performance_mode(AudioPerformanceMode::LowLatency)
                 .sharing_mode(sharing)
                 .data_callback(Box::new(callback))